A Sky Full of Ghosts
A Sky Full of Ghosts is the fourth episode of Cosmos: A Spacetime Odyssey. It first aired March 30, 2014 on Fox and March 31 on National Geographic. The episode explores black holes, tracing ideas from John Michell’s concept of an invisible star to the discovery of Cygnus X-1. The title points to how light from distant stars takes so long to reach Earth that we may be seeing objects as they were long ago.
Neil deGrasse Tyson explains how we learn about the universe by looking back in time, using light to study the Big Bang and the age of the cosmos. The episode covers contributions from scientists like Isaac Newton, William Herschel, Michael Faraday, James Clerk Maxwell, and Albert Einstein, and explains how gravity is a warping of space and time. It introduces the idea of dark stars and shows how black holes can trap light, with Cygnus X-1 as a real example. An animated Ship of the Imagination illustrates spacetime warping and time dilation near a black hole, hinting at strange possibilities such as time travel. The show ends by noting that William Herschel’s son, John Herschel, continued his father’s work.
Animated scenes feature William and John Herschel, with Patrick Stewart voicing William. The episode received positive reviews for its production value, but drew about 3.9 million live viewers in the U.S. and a 1.5/4 rating in the 18–49 demographic.
This page was last edited on 3 February 2026, at 13:53 (CET).